This is soooo relevant. I have bought a Haynes manual for virtually all my motorbikes and cars and have used some a lot, notably the ones for older style Minis and BMW 'R' series boxer engined motorbikes. I am pleased to say that I haven't bought one for the Moto Guzzi or the Isuzu Trooper yet as they are, respectively, still under warranty and 12 years old. If I have to do something to the Trooper that requires a Haynes Manual then I would prefer to spend the money on a replacement vehicle as my back/legs/knuckles/patience couldn't stand the stress and strain of outdoor working in all weathers.
Haynes have been useful for me and have saved me loads of money but our relationship is now at an end.